Block modification of rod-shaped pi conjugated carbon frameworks with donor and acceptor groups toward highly fluorescent molecules: synthesis and emission characteristics.

To create organic molecules that are highly fluorescent at a longer wavelength region, we investigated the synthesis (using Pd-catalyzed cross-coupling) and photophysical properties (Phi(f), lambda(em), tau, lambda(abs), and epsilon) of the following pi conjugated molecular rods consisting of p-phenyleneethynylene units modified by donor (OMe) and/or acceptor (CN) groups: (1) side-donor modification systems (SD systems), (2) side-acceptor modification systems (SA systems), and (3) systems consisting of a donor block and an acceptor block (BL systems). As a consequence, very high Phi(f) values (>0.95) were obtained for BL systems. Bathochromic shifts of lambda(em) for the same pi conjugation length were largest for BL systems. Thus we succeeded in creating highly efficient light emitters at a longer wavelength region by block modification (e.g., Phi(f) = 0.97, lambda(em) = 464 nm for ). Considerably intense solid emission (Phi(f) approximately 0.5) at a longer wavelength region (500-560 nm) was also found for BL systems. It has been found that and exhibit interesting two photon absorption characteristics.